1. Field of the Invention
The present invention relates to an un-interruptible power supply (UPS) and, more particularly, to a UPS with indication of battery internal resistance.
2. Description of the Related Art
Modern people use computers to handle information at work and in daily life or use servers to process network information exchange. Hence, it is crucial to keep computer and servers operating under a stable condition. To prevent loss arising from unexpected shutdown of computers and servers during mains power failure, conventionally, UPSs are provided to supply short-term power to computers and servers for storing data generated in operation and avoiding any form of loss out of missing information during mains power failure. Speaking of development of UPS, battery may be a current focus of UPS development.
As disclosed in U.S. Pat. No. 6,094,030 (hereinafter GUNTHORPE), internal resistance and capacity of a backup battery pack are monitored. The internal resistance of each battery of the backup battery pack is detected and is transmitted to a remote server for calculation to determine status of the internal resistance of each battery. Frequency of charging each battery can be independently adjusted to prevent the battery from being over-charged. However, GUNTHORPE can only adjust the battery-charging frequency for battery overcharge avoidance without providing any kind of alarm and report, making users unaware of current condition of the batteries.
As disclosed in U.S. Pat. No. 7,902,828 (hereinafter HUANG), a warning method for monitoring battery performance according to internal resistance of power supply includes coupling a first power transistor as or as part of a first external load in series with the battery, coupling a second power transistor as or as part of a second external load in series with the battery, and repeatedly conducting each power transistor to draw a transient large current from the battery while sampling the voltage across the battery and voltage across the load, from which the internal resistance of the battery can be determined. The internal resistance of the battery can then be compared with a predetermined nominal value to issue a warning if the battery is weak.
Although HUANG can determine if the battery is good for operation, the transient large current must be repeatedly acquired and such necessity requires battery to be discharged a couple of times, which in turn deteriorates battery performance. Structural complication also arises from the additionally equipped first power transistor, first external resistor, second power transistor and second external resistor. Additionally, the predetermined nominal value is configured based on type of battery, and under the circumstance of unstable battery operation, the comparison between the internal resistance and the predetermined nominal value easily leads to an incorrect determination result.